Water-soluble substrates are gaining wider acceptance for use as packaging materials. Packaging materials include films, sheets, blown or molded hollow bodies (i.e. sachets, pouches, and tablets), bottles, receptacles and the like. Often, water-soluble substrates, when used in the preparation of certain types of these articles such as sachets and pouches, disintegrate and/or become sticky when exposed to small amounts of water or high humidity. This can make them unsuitable for usage in the packaging and storage of the compositions contained therein.
The most common consumer complaint for water-soluble pouches is linked to unwanted pouch dissolution when accidentally exposed to small amounts of water, such as when water gets inside the outer packaging in which the pouches are sold and stored after purchase, from wet hands, high humidity, leaking sinks or pipes during storage. This may cause the water-soluble pouches to leak prior to use and/or stick together. The second most frequent complaint is that of the water-soluble pouch failing to fully dissolve upon use. Thus, there remains an unmet need for water-soluble substrates and articles made therefrom, such as sachets and pouches, which have improved resistance to dissolution against exposure to small amounts of water yet can subsequently dissolve very quickly when immersed in an aqueous solution, such as rinse and/or wash water.
Various methods are known in the art to retard the dissolution of water-soluble substrates, typically involving coating the water-soluble substrate with a material which is water-insoluble. For example, U.S. Pat. No. 6,509,072 describes a water-soluble substrate comprising a barrier coating. The barrier coating is a polymeric film which forms a continuous film on the water-soluble substrate. Another example of a barrier coating is described in WO 01/23460, assigned to Kao Corporation, wherein a surface of the water-soluble substrate is coated with a particulate or fibrous water-insoluble material wherein the amount of the water-insoluble material used is 0.1-80 parts per 100 parts by weight of the water-soluble film. In use (which typically involves immersing the water-soluble substrate in an aqueous solution) however, it is desired that the coating quickly disintegrates. Depending on the use of the water-soluble substrate, the aqueous solution into which the substrate or an article comprising the substrate is to be immersed, may have a pH which is acid or alkaline. Although coatings of the prior art may provide sufficient resistance against accidental water contact (at a neutral pH), they may not be able to quickly disintegrate or dissolve when immersed in acid or alkaline solutions.
It is therefore an aspect of the present invention to provide water-soluble substrates which improves resistance to dissolution at neutral pH, yet can dissolve very quickly when immersed in an aqueous solution having an acid or an alkaline pH.